1. Field of the Invention
Cellulosic-reinforced polyolefin composites which exhibit markedly reduced water absorption are provided. More specifically, the improved composites of the invention comprise a cellulosic filler with a polyolefin matrix polymer comprised of a high density polyethylene resin and a silane copolymer at prescribed weight ratios.
2. Description of the Prior Art
Usage of Cellulosic-reinforced composites and, more specifically, plastic composites has grown in recent years as consumers discover the advantages of these products compared to wood. In view of their physical properties and low maintenance they are increasingly being utilized for installations in environments which are unfavorable to the use of wood, e.g., where cracking, warping, rotting, attack by insects typically would be expected.
Furthermore, cellulosic-reinforced plastic components are not limited to utilitarian applications, i.e., for extruded profiles such as decking boards and the like. They are equally useful for the manufacture of injection molded or compression molded decorative parts, such as might be used for interior or exterior trim.
Numerous plastic resins including high density polyethylene (HDPE); low-density polyethylene (LDPE); polyvinyl chloride; polypropylene; ethylene-vinyl acetate; acrylonitrile-butadiene-styrene (ABS); polystyrene has been used to form composites with cellulosic fillers such as sawdust; wood chips; wood fibers; wood particles; ground wood; wood flour; wood flakes; rice hulls; coconut shells and peanut shells; bagasse and plant fibers.
The amount of cellulosic filler used will vary depending on the particular resin and fiber being used and the intended application. In general, however, about 40-60% cellulosic filler is utilized for extruded deck profiles and lower filler loadings, on the order of 20-30%, are used for pieces which are molded.
A common problem associated with the use of wood-filled composites for exterior applications is their tendency to absorb water. Water absorption swells the fibers at the surface of the composite which in turn causes stresses that can lead to cracking. It would be highly advantageous if composites having good physical properties, moldability and reduced water absorption were available. These and other advantages are obtained with the composites of the present invention.